A VFD overcurrent fault can stop a motor before it has completed a single revolution—or wait until the machine has been running normally for half an hour.

Both situations may display the same basic fault:

• OC
• OCF
• Overcurrent
• Output overcurrent
• Motor overcurrent
• F0001
• F07801
• another manufacturer-specific code

The wording varies, but the basic meaning is similar: the drive detected output current above an allowed limit and disabled its power stage to protect itself.

The fault code alone is not enough to identify the cause.

The most useful question is:

Exactly when does the VFD trip?

An overcurrent fault immediately after pressing Start points toward a different group of problems than one occurring during acceleration, at constant speed or during deceleration.

This guide uses that timing to narrow the diagnosis systematically.

What Does a VFD Overcurrent Fault Mean?

A VFD creates a controlled three-phase output using power semiconductors such as IGBTs.

The drive continuously monitors motor current. If the measured current rises beyond a protective threshold, the VFD disables its output—often almost immediately.

This protects the drive against conditions such as:

• motor-cable short circuits;
• earth faults;
• locked rotors;
• severe mechanical jams;
• excessively fast acceleration;
• incorrect motor parameters;
• unstable motor control;
• internal power-stage faults.

An overcurrent trip is normally an immediate protective response. It is different from an overload fault, which generally models excessive heating accumulated over time. Schneider Electric, for example, distinguishes immediate overcurrent shutdown from power-stage overload, where thermal loading is evaluated over a longer period.

Overcurrent Is Not the Same as Overload

The two terms are often used interchangeably, but they describe different fault behaviour.

Overcurrent

Overcurrent normally means current increased extremely quickly or exceeded a high instantaneous limit.

Typical causes include:

• short circuit;
• earth fault;
• locked rotor;
• sudden load impact;
• unsuitable acceleration;
• incorrect control parameters;
• failed VFD power stage.

Overload

Overload usually means the motor or drive carried excessive current long enough to create unacceptable thermal stress.

Typical causes include:

• sustained excessive mechanical load;
• undersized motor;
• undersized drive;
• poor cooling;
• repeated starts;
• operation above the permitted duty cycle.

A conveyor that jams solid may create an immediate OC fault.

A conveyor that is merely overloaded may continue running for several minutes before producing OL or motor-overload protection.

That distinction prevents a great deal of wasted troubleshooting.

Quick Timing-Based Diagnostic Table

Use this table to choose the first checks. Do not treat it as a substitute for the drive’s complete fault record.

Before Resetting the Fault

Do not begin by repeatedly pressing RESET.

First record:

• the complete fault code;
• any subcode or extended diagnostic number;
• output frequency at the moment of trip;
• motor current;
• DC-bus voltage, if available;
• whether the motor was accelerating or decelerating;
• speed reference;
• torque reference;
• operating direction;
• load condition;
• recent wiring or parameter changes.

Many VFDs store several previous faults together with operating values. That history may show that the current was already rising before the final trip.

A fault reset clears the active indication.

It does not repair the cause.

Electrical Safety Before Testing

VFDs can retain dangerous DC voltage after incoming power has been disconnected.

Before touching the drive, motor cable or motor terminals:

1. Stop the machine safely.
2. Isolate all electrical and mechanical energy sources.
3. Follow the site’s lockout and tagout procedure.
4. Wait for the manufacturer’s specified discharge time.
5. Verify the absence of voltage with suitable test equipment.
6. Confirm that the motor cannot be driven by the load.

Do not perform insulation-resistance testing through the VFD output terminals. Official drive procedures require the motor cable to be disconnected from the VFD before insulation testing, because the test voltage can damage the drive electronics.

1. Overcurrent Immediately After Pressing Start

When the drive trips the instant a Start command is given, the fault is likely connected to the motor circuit, starting condition or VFD power stage.

There has not been enough time for a normal thermal overload to develop.

Most Likely Causes

Phase-to-phase short circuit

Two motor conductors may be touching because of:

• damaged insulation;
• crushed cable;
• contamination in the terminal box;
• loose conductor strands;
• incorrect terminal links;
• damaged winding insulation.

The moment the VFD produces output voltage, current rises sharply and the drive trips.

Phase-to-earth fault

A motor winding or cable conductor may be leaking to the motor frame, cable shield or protective earth.

Possible causes include:

• water inside the motor;
• damaged cable insulation;
• overheated windings;
• conductive dust;
• damaged terminal insulation;
• incorrect shield termination touching a live terminal.

Some drives report this as an earth-fault code rather than overcurrent. Others may initially trip on the same high-current protection threshold.

Locked rotor

A motor that cannot rotate may demand very high current immediately.

Check for:

• seized bearing;
• jammed pump;
• blocked conveyor;
• frozen gearbox;
• mechanically engaged brake;
• product trapped in the machine;
• incorrectly assembled coupling.

Incorrect star/delta connection

The motor terminal links must match both the motor nameplate and the VFD output voltage.

For example:

• a 230/400 V Δ/Y motor normally operates in star at 400 V;
• a 400/690 V Δ/Y motor normally operates in delta at 400 V.

Connecting a winding for the wrong voltage can produce inadequate torque or excessive current.

Motor brake is not releasing

On a geared motor or hoist, the VFD may energise the motor before the mechanical brake opens.

The motor attempts to accelerate against the brake and trips on overcurrent.

Check:

• brake supply voltage;
• brake rectifier;
• release timing;
• brake coil;
• mechanical air gap;
• PLC sequence;
• VFD brake-control output.

Output contactor switches at the wrong time

A contactor between the VFD and motor should not normally open or close while the drive is actively producing output unless the complete system is specifically designed for it.

Closing a motor contactor after the VFD has already enabled its PWM output can create a severe current transient.

Excessive DC injection or starting boost

Some drives apply DC braking or magnetising current before acceleration.

Incorrect values can create excessive current before the shaft begins moving.

Internal VFD failure

A damaged IGBT, gate-driver circuit or current-sensing circuit may produce an immediate trip, especially if the fault remains when the motor circuit has been correctly isolated.

Step-by-Step Fix: Immediate OC Fault

Step 1: Check whether the shaft can rotate

Safely isolate the machine and verify that the motor and load are not mechanically locked.

Do not force a shaft that is connected to a hazardous or stored-energy system.

Step 2: Inspect the terminal box

Check:

• loose strands;
• damaged links;
• moisture;
• carbon tracking;
• correct star/delta arrangement;
• tight terminals;
• signs of overheating.

Step 3: Inspect the motor cable

Pay particular attention to:

• moving cable carriers;
• sharp bends;
• crushed sections;
• areas near cable glands;
• oil- or chemical-damaged insulation;
• recently modified connections.

Step 4: Measure winding resistance

With the motor safely isolated and disconnected as required, compare the resistance between:

• U–V;
• V–W;
• W–U.

The values should be reasonably balanced. A major difference suggests a winding, connection or cable problem.

Very low motor winding resistance is normal on larger motors, so ordinary multimeter readings can be difficult to interpret. The comparison between phases is often more useful than the absolute number.

Step 5: Perform insulation testing correctly

Disconnect the cable from the VFD before using an insulation-resistance tester.

Test the motor and cable according to the motor and drive manufacturers’ instructions. Never apply a megohmmeter test voltage to connected VFD output electronics.

Step 6: Check brake release

Confirm the brake releases before torque is demanded.

Step 7: Verify motor data and connection

Confirm:

• rated voltage;
• rated current;
• rated frequency;
• rated speed;
• power;
• star/delta links;
• control mode.

Step 8: Perform an approved no-motor test

Only do this if the VFD manufacturer permits operation with the motor disconnected.

If the drive trips immediately on overcurrent with its output safely disconnected, suspicion shifts toward the VFD power stage, current sensors or internal control electronics.

2. Overcurrent During Acceleration

An OC fault during acceleration is one of the most common VFD problems.

The motor begins turning but trips before reaching commanded speed.

In this case, the motor is usually demanding more torque—and therefore more current—than the drive can safely provide.

Official drive documentation commonly recommends selecting an acceleration ramp that keeps current below the configured current limit.

Most Likely Causes

Acceleration time is too short

A short ramp demands rapid speed change.

The torque required to accelerate a rotating system depends on its inertia and acceleration rate. A large fan, centrifuge, roller or loaded conveyor may require substantial torque even when it rotates freely.

The faster you ask it to accelerate, the more current the motor generally needs.

High-inertia load

High-inertia applications include:

• large fans;
• flywheels;
• centrifuges;
• winding rolls;
• large drums;
• heavy conveyors;
• mixers containing dense material.

A motor may be correctly sized for continuous operation but still need more acceleration time.

The process starts under load

Some machines should start unloaded but occasionally retain material, pressure or mechanical tension from the previous cycle.

Examples include:

• pump starting against high pressure;
• conveyor starting full of product;
• compressor starting without unloading;
• mixer starting with solidified material;
• crusher starting with material trapped inside.

Incorrect motor parameters

Vector-control algorithms depend on accurate motor information.

Incorrect data can produce excessive flux, poor current control and unstable torque.

Verify:

• motor rated current;
• rated voltage;
• base frequency;
• rated speed;
• power factor;
• rated power;
• motor type.

Siemens troubleshooting guidance for motor overcurrent includes checking motor data, motor commissioning, motor-cable faults and acceleration-ramp settings.

Autotune was not completed

A vector-control drive may need motor identification or autotuning.

If the drive uses generic values rather than the real motor characteristics, low-speed current control can be poor.

Excessive low-speed voltage boost

In basic volts-per-hertz control, additional low-frequency voltage may be used to compensate for winding resistance.

Too much boost can over-flux the motor and create high current at the start of acceleration.

Current or torque limit is configured incorrectly

A current limit set too low normally causes the drive to extend the ramp or hold speed, depending on the model. Poorly coordinated control settings can still produce unstable operation or a trip when the current rises faster than the control loop can limit it.

VFD is undersized

Check the VFD’s current rating, not just its kilowatt rating.

The drive may be unsuitable because of:

• inadequate continuous current;
• insufficient overload capacity;
• high ambient-temperature derating;
• high carrier-frequency derating;
• heavy-duty application requirements.

Step-by-Step Fix: OC During Acceleration

Step 1: Record the trip frequency and current

Does the fault occur at:

• 0–2 Hz;
• 10 Hz;
• halfway through the ramp;
• almost at full speed?

A fault at very low frequency points more strongly toward starting boost, brake release or motor data.

A fault later in the ramp points more strongly toward inertia or process load.

Step 2: Increase acceleration time

Make a controlled adjustment rather than changing several parameters at once.

For example, if the current ramp is 3 seconds, try 6 or 10 seconds if the machine process permits it.

Do not lengthen the ramp beyond the motor’s safe stalled or low-speed thermal capability.

Step 3: Run the machine unloaded where possible

If the motor accelerates normally without the process load, the drive and motor circuit may be healthy.

Focus on:

• load inertia;
• jamming;
• product buildup;
• pressure;
• gearbox resistance.

Step 4: Verify brake timing

Confirm the brake is mechanically released before the drive develops significant torque.

Step 5: Confirm motor nameplate data

Correct any wrong parameter and repeat the manufacturer’s commissioning procedure.

Step 6: Run autotune

Follow the drive manual carefully. Some identification procedures rotate the motor; others are stationary.

Disconnecting the load may be necessary for a rotating autotune.

Step 7: Reduce excessive boost

Do not reduce it blindly. Too little boost may prevent the motor from starting.

Step 8: Check drive sizing

Compare the recorded peak current with:

• motor nameplate current;
• VFD rated output current;
• VFD overload rating;
• application duty.

A larger drive may be required if the real acceleration torque exceeds the installed unit’s capacity.

3. Overcurrent at Constant Speed

The motor reaches its target speed and runs normally—then suddenly trips on overcurrent.

This is less likely to be a simple acceleration-ramp problem.

The fault often indicates a sudden change in load, intermittent cable problem or unstable control condition.

Most Likely Causes

Intermittent mechanical jam

The machine may occasionally encounter:

• oversized product;
• material buildup;
• tight bearing;
• damaged chain;
• bent guide;
• pump blockage;
• gearbox tooth damage;
• sticking valve;
• periodic load impact.

The average current may look normal while brief peaks exceed the drive’s protection threshold.

Load increases sharply with speed or process demand

Fans and centrifugal pumps require substantially more power as speed increases.

A motor may run normally at 40 Hz but become heavily loaded near 50 or 60 Hz.

The drive is not necessarily faulty. The process may simply demand more torque than the motor or VFD can provide.

Intermittent motor-cable fault

Vibration, heat or movement can cause damaged insulation to fail only occasionally.

A cable may test correctly while stationary and fault when:

• the machine moves;
• the cable carrier bends;
• the motor becomes hot;
• moisture enters a damaged gland;
• a loose conductor shifts.

Loose motor terminal

A loose connection can produce arcing, phase imbalance and sudden current disturbance.

Inspect for:

• discoloration;
• melted insulation;
• damaged terminal studs;
• loose crimp lugs;
• carbon deposits.

Incorrect vector-control tuning

Poor motor-model parameters can make current or torque control unstable under changing load.

This is especially likely after:

• motor replacement;
• drive replacement;
• copied parameters;
• skipped autotune;
• incorrect encoder setup.

Encoder or feedback problem

In closed-loop control, intermittent encoder signals can make the drive calculate incorrect speed error and demand excessive corrective torque.

Check:

• encoder supply;
• connector;
• cable shield;
• pulse quality;
• mechanical coupling;
• configured pulse count;
• direction.

Resonance or torsional oscillation

At one speed, the motor and load may enter mechanical resonance. Torque oscillations can then produce current peaks.

If the fault repeatedly occurs in a narrow speed band, inspect the mechanical system and consider a skip-frequency function only after confirming there is no damaged machinery.

Step-by-Step Fix: OC at Constant Speed

Step 1: Trend current rather than watching the display

A keypad display may update too slowly to show a short current spike.

Use:

• VFD trace function;
• PLC data logging;
• manufacturer commissioning software;
• suitable current measurement equipment.

Trend current against:

• speed;
• torque;
• process pressure;
• conveyor load;
• vibration;
• fault time.

Step 2: Identify the exact machine event

Does the trip occur when:

• a valve opens;
• product enters the conveyor;
• a cutter engages;
• a pump reaches pressure;
• another motor starts;
• direction changes;
• a brake operates?

Step 3: Inspect mechanical components

Check bearings, couplings, chains, belts, gears and process obstructions.

Step 4: Check all three motor connections

Inspect terminals and cable condition.

Step 5: Verify motor tuning

Repeat identification if the motor or drive has been replaced.

Step 6: Inspect feedback signals

For encoder systems, review speed feedback for sudden jumps or dropouts.

Step 7: Reduce the maximum operating speed temporarily

If current remains acceptable at a lower speed, calculate whether the load demand near maximum speed exceeds the motor’s available power.

Do not use permanent speed reduction to hide a developing mechanical fault.

4. Overcurrent During Deceleration

A deceleration fault is often assumed to be overvoltage because the motor regenerates energy into the DC bus.

That is common—but an actual overcurrent fault during deceleration can also occur.

Drive manuals instruct users to select a ramp-down time that avoids both excessive regenerated voltage and excessive current.

Most Likely Causes

Deceleration time is too short

Rapid deceleration requires braking torque.

The motor becomes a generator, and the VFD must control the resulting current. A very aggressive ramp can exceed the drive’s current capability.

High-inertia load

A heavy rotating load resists speed change.

Examples include:

• flywheels;
• centrifuges;
• large fans;
• rollers;
• winding machines;
• saw blades;
• drums.

Overhauling load

In applications such as hoists or downhill conveyors, the load may actively drive the motor.

The VFD must control both speed and regenerated energy.

DC injection braking is too aggressive

Some drives inject DC current into the motor near zero speed to create braking torque.

Too much current or an unsuitable DC-braking period can trigger overcurrent. Yaskawa documentation specifically notes that an OC condition during DC-injection stopping may require changing the relevant braking and baseblock timing.

Torque direction reverses too quickly

A command that changes directly from forward torque to reverse torque can produce a large current transient.

Mechanical brake engages too early

If the brake closes before the motor has stopped or before the VFD has removed torque correctly, it can produce a sudden current increase.

Vector-control instability

Incorrect motor data or feedback can produce excessive braking-current demand.

Step-by-Step Fix: OC During Deceleration

Step 1: Confirm the code really is overcurrent

Do not confuse:

• OC: overcurrent;
• OV: DC-bus overvoltage;
• OL: overload;
• braking-resistor overload.

The solutions differ.

Step 2: Increase deceleration time

If the process permits, extend the ramp and test again.

If the fault disappears, the original deceleration demand exceeded the system’s capability.

Step 3: Review the load

Determine whether the load:

• coasts naturally;
• drives the motor;
• contains high inertia;
• changes direction;
• drops under gravity.

Step 4: Check DC-braking settings

Review:

• DC-brake current;
• start frequency;
• braking duration;
• zero-speed hold current;
• baseblock time.

Step 5: Check brake-control timing

For a mechanical brake, verify that the release and engagement sequence matches the drive manufacturer’s recommended arrangement.

Step 6: Review torque and speed-loop tuning

Poorly tuned closed-loop systems may overshoot during stopping.

Step 7: Consider the correct braking solution

Depending on the application, the system may need:

• a longer stop;
• braking resistor;
• braking unit;
• regenerative drive;
• mechanical brake coordination.

A braking resistor primarily controls DC-bus energy. It does not automatically cure every deceleration overcurrent fault.

5. Overcurrent With the Motor Disconnected

This is one of the most useful diagnostic situations—but also one of the easiest to test incorrectly.

If the motor and cable have been disconnected from the VFD output and an approved no-load Start test still produces an overcurrent fault, the external motor circuit is no longer the main suspect.

Possible causes include:

• failed IGBT;
• shorted output power module;
• defective gate driver;
• current-sensor fault;
• damaged control board;
• incorrect current calibration;
• internal contamination;
• previous surge damage.

Schneider’s overcurrent documentation identifies motor short circuits as an external cause; once the motor circuit has been properly removed from the test, a persistent trip shifts suspicion toward the drive itself.

Important Testing Limitation

Not every VFD is intended to run normally without a connected motor.

Some drives may report:

• output phase loss;
• motor missing;
• autotune failure;
• abnormal current measurement.

Follow the exact model’s service procedure.

Do not assume that any unexpected code during a no-motor test proves the drive is defective.

Step-by-Step Fix: OC With Motor Disconnected

Step 1: Confirm safe isolation

Verify the motor cable is disconnected from U, V and W—not merely disconnected at the motor while leaving a potentially faulty cable attached to the drive.

Step 2: Check for conductive debris

Inspect for:

• metal filings;
• insects;
• moisture;
• carbon contamination;
• damaged terminal insulation;
• loose strands near output terminals.

Step 3: Review the fault before enabling output

Does the fault appear:

• immediately after power-up;
• when the drive becomes ready;
• only after Start;
• only above a certain frequency?

A fault before any output command strongly suggests an internal or sensing problem.

Step 4: Restore default motor parameters only when appropriate

Parameter corruption is less common than wiring faults, but incorrect control data can sometimes cause abnormal behaviour.

Back up the current parameter set before changing anything.

Step 5: Follow the manufacturer’s power-stage test

Some manufacturers provide diode-check or semiconductor-test procedures.

Do not improvise resistance measurements on a charged drive.

Step 6: Replace or repair the VFD if internal failure is confirmed

Before installing the replacement, inspect the motor and cable thoroughly.

A shorted cable that destroyed the original VFD can destroy the replacement too.

6. Overcurrent Under Heavy Mechanical Load

If the motor runs successfully while unloaded but trips when the real process load is applied, the problem is likely related to torque demand, mechanical resistance or equipment sizing.

Most Likely Causes

Genuine mechanical overload

Examples include:

• conveyor carrying too much product;
• mixer overfilled;
• pump operating outside its intended range;
• compressor starting loaded;
• crusher fed too aggressively;
• blocked filter;
• high process pressure;
• cutting tool engaging too deeply.

Binding machinery

The load may not be intentionally excessive. Mechanical friction may have increased because of:

• worn bearings;
• poor lubrication;
• misalignment;
• overtightened belts;
• damaged gearbox;
• bent shaft;
• dragging brake;
• contaminated product path.

Motor is undersized

The VFD cannot create unlimited torque from an undersized motor.

If the motor must operate above rated current to perform the process continuously, the motor is not correctly selected for that duty.

VFD is undersized

The VFD’s current rating must suit:

• motor current;
• required starting torque;
• overload duration;
• carrier frequency;
• ambient temperature;
• enclosure conditions;
• heavy- or normal-duty classification.

Motor cooling is poor at low speed

A standard motor with a shaft-mounted fan may develop rated torque at low speed while receiving very little cooling airflow.

Although this more commonly leads to thermal overload, rising winding resistance and unstable operation can contribute to current problems.

Torque limit is too high

Increasing the torque or current limit can allow the motor to place excessive stress on the machine before the VFD trips.

Limits should protect the motor and mechanical system—not merely prevent nuisance shutdowns.

Step-by-Step Fix: OC Under Load

Step 1: Measure no-load current

Run the motor without the mechanical load only when safe and practical.

If no-load current is already abnormally high, investigate:

• motor connection;
• motor data;
• winding condition;
• control mode;
• voltage boost.

Step 2: Measure loaded current

Compare the value with:

• motor nameplate current;
• VFD continuous-current rating;
• VFD overload capacity.

Step 3: Observe how current changes with the process

Does it rise with:

• pressure;
• product quantity;
• speed;
• temperature;
• belt tension;
• valve position?

Step 4: Inspect the driven machine

Do not assume an electrically healthy motor proves the machine is mechanically healthy.

Step 5: Review motor and VFD sizing

Use torque and duty requirements, not only kilowatts.

Step 6: Reduce the process load temporarily

If current falls predictably and the fault disappears, the drive is responding to the real mechanical demand.

Step 7: Correct the load rather than raising protection

Increasing the current limit may only delay failure or move the damage into the motor, gearbox or process machinery.

Other Causes That Can Appear in Any Operating Stage

Incorrect motor cable length or output filter

Long motor cables add capacitance to the VFD output.

The drive must repeatedly charge and discharge that capacitance during PWM switching. Excessive cable length, an unsuitable filter or an incorrect carrier frequency can increase output current.

Follow the VFD manufacturer’s maximum cable-length and filter requirements.

Unsuitable switching frequency

Higher carrier frequency increases switching activity and may affect available drive current.

Some VFDs require output-current derating at higher switching frequencies.

Multiple motors on one VFD

The drive sees the combined current of all connected motors.

Possible issues include:

• total current exceeding the VFD rating;
• one motor starting while others are running;
• unequal motor characteristics;
• output contactors switching under load;
• inadequate individual motor protection.

Direction reversal without sufficient delay

Changing directly from forward to reverse can create a severe braking and acceleration demand.

Use the intended ramp and control sequence.

Unstable incoming power

Low or unbalanced supply voltage usually causes other fault codes first, but severe input problems can destabilise the DC bus and reduce the drive’s ability to control current under load.

Wrong motor type selected

A drive configured for a permanent-magnet motor but connected to an induction motor—or the reverse—may produce immediate or unstable current.

A Complete Diagnostic Workflow

Step 1: Read the exact code

Do not troubleshoot from the letters OC alone.

Record the complete manufacturer-specific code and subcode.

Step 2: Determine when it trips

Choose the closest category:

• immediately after Start;
• during acceleration;
• at constant speed;
• during deceleration;
• under heavy load;
• with no motor connected.

Step 3: Check recent changes

Ask whether anyone recently:

• replaced the motor;
• changed the VFD;
• edited parameters;
• changed terminal links;
• replaced a cable;
• modified acceleration time;
• adjusted a brake;
• increased machine speed.

Yesterday’s improvement is often today’s fault.

Step 4: Inspect the mechanical system

Confirm the motor can rotate and the process is not jammed.

Step 5: Check motor nameplate data

Verify every relevant parameter.

Step 6: Measure actual current

Use the VFD monitor or suitable true-RMS equipment approved for PWM motor circuits.

Step 7: Inspect all power connections

Check:

• input supply;
• VFD output terminals;
• isolators;
• output contactors;
• cable glands;
• motor terminals;
• star/delta links.

Step 8: Test the motor and cable

Disconnect them correctly before insulation testing.

Step 9: Separate motor, cable and drive

Testing them independently is far more useful than replacing parts randomly.

Step 10: Change one parameter at a time

Record original and new values.

Step 11: Test through the full operating cycle

A successful unloaded start does not prove the machine is repaired.

Parameters Commonly Connected to Overcurrent Faults

The names and numbers vary by manufacturer, but check:

• motor rated current;
• motor rated voltage;
• motor rated frequency;
• motor rated speed;
• motor rated power;
• motor type;
• acceleration time;
• deceleration time;
• current limit;
• torque limit;
• starting torque boost;
• DC-injection braking;
• control mode;
• slip compensation;
• carrier frequency;
• autotune data;
• encoder parameters;
• brake-control timing;
• maximum output frequency.

Do not copy parameters from another VFD merely because the motor power is similar.

Two 7.5 kW motors can have different rated currents, speeds and electrical characteristics.

Common Mistakes That Make the Fault Worse

Avoid:

• repeatedly resetting an unexplained OC fault;
• increasing current limits blindly;
• shortening acceleration to improve production speed;
• bypassing a mechanical brake interlock;
• operating output contactors while the VFD is enabled;
• testing insulation through the drive;
• installing a larger VFD without checking the motor cable;
• assuming the motor is healthy because it rotates by hand;
• replacing the VFD before checking the load;
• running an unsafe no-motor test;
• ignoring an intermittent cable fault.

The VFD trips quickly because semiconductor damage can occur quickly.

Treat that speed as protection, not inconvenience.

When Should You Suspect the VFD Itself?

Internal drive failure becomes more likely when:

• overcurrent appears before a run command;
• the fault remains with the motor and cable safely disconnected;
• the drive trips with a known-good motor and cable;
• current readings are impossible or unstable;
• there is visible or burnt power-stage damage;
• the fault began after a severe short circuit;
• the fault cannot be reset using the documented method;
• one output phase behaves differently;
• the manufacturer’s semiconductor test fails.

Even then, check the original motor circuit before installing another VFD.

The first drive may have failed for a reason.

Why the Timing of the Fault Matters

A VFD overcurrent fault is not one problem.

It is a protective reaction to several possible problems.

The trip timing dramatically narrows the search:

• Immediately after Start: inspect motor wiring, insulation, terminal links, brake and power stage.
• During acceleration: check ramp time, inertia, motor data, autotune and starting load.
• At constant speed: look for intermittent load changes, cable faults, loose connections and unstable control.
• During deceleration: review braking current, ramp time, regeneration and brake timing.
• With the motor disconnected: follow the manufacturer’s test procedure and investigate internal VFD faults.
• Under heavy load: measure real torque demand and confirm motor and drive sizing.

A better diagnosis begins with evidence, not parameter guessing.

Record when the fault occurs. Separate the motor, cable, drive and mechanical load. Test each part safely and methodically.

The Reset button may clear the screen in one second.

A proper repair explains why the current became too high in the first place.